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[Cyclin dependent kinase inhibitors and replicative senescence]
L M Gerland1, M Ffrench, J P Magaud
1Laboratoire de cytologie analytique (Inserm U 453), faculté de médecine, 69373 Lyon, France.
Abstract:
Replicative senescence is defined for human diploid fibroblasts in culture as a cell growth arrest appearing beyond 50 +/- 10 population doublings and associated with telomeres' shortening. This phenomenon shows an increased expression of growth cell inhibitors: p21Waf1 described as an universal CDK inhibitor and p16INK4a as a specific inhibitor for both G1 phase kinases CDK4 and CDK6. The cell proliferation inhibitor p14ARF, product of INK4a/ARF locus is involved in replicative senescence too. Overexpression or homozygotic deletion of these inhibitors demonstrated their role in senescence induction. These proteins are involved in two different metabolic pathways, the first including p53, represented by E2F, ARF, MDM2, p53, p21Waf1, and the second concerning pRb and p16INK4a. These two pathways present numerous interactions and the polymerase (PARP) in relation with p53 and activated by telomere shortening might represent via p21Waf1 a link between this shortening and cell cycle control. An another metabolic pathway involving PTEN and p27KIP1 is discussed in senescent-like phenotype induction, but its activity in replicative senescent is uncertain.
Insights
Replicative senescence in human cells involves cell cycle arrest due to telomere shortening. Key inhibitors like p21Waf1 and p16INK4a are upregulated, linking telomere length to cell proliferation control.
Area of Science:
- Cell Biology
- Molecular Biology
- Gerontology
Background:
- Replicative senescence is a state of irreversible cell growth arrest in human diploid fibroblasts.
- This process occurs after a finite number of cell divisions (around 50 population doublings) and is linked to telomere shortening.
- Senescence involves the upregulation of specific cell cycle inhibitors.
Purpose of the Study:
- To investigate the role of cell cycle inhibitors in replicative senescence.
- To elucidate the molecular pathways involved in linking telomere shortening to cell cycle arrest.
- To understand the interactions between different protein pathways in the senescence process.
Main Methods:
- Analysis of human diploid fibroblasts undergoing replicative senescence.
- Assessment of population doublings and telomere length.
- Quantification of cell cycle inhibitor expression (p21Waf1, p16INK4a, p14ARF).
- Examination of protein-protein interactions within key signaling pathways (p53, pRb).
Main Results:
- Replicative senescence is characterized by cell growth arrest and telomere shortening.
- Expression of cell cycle inhibitors p21Waf1, p16INK4a, and p14ARF is increased.
- These inhibitors are part of distinct but interacting pathways involving p53 and pRb.
- Polymerase (PARP) activation by telomere shortening may link telomere length to cell cycle control via p21Waf1.
Conclusions:
- Telomere shortening triggers replicative senescence through the upregulation of cell cycle inhibitors.
- The p53 and pRb pathways, along with PARP activation, play crucial roles in this process.
- p21Waf1 acts as a potential mediator connecting telomere shortening to cell cycle regulation.